1. Field of the Invention
The present invention relates to an optical disk apparatus and, more particularly, to an optical disk apparatus capable of adjusting a dislocation of an optical axis.
2. Description of the Related Art
A prior art optical disk apparatus using a separate optical-type access mechanism has such a structure as shown in FIG. 7. In FIG. 7, numeral 70 designates a stationary optical unit. On the side of the stationary optical unit 70, a mobile optical unit 71 is installed to scan an optical disk. The mobile optical unit 71 comprises a rotary mirror 72, a lens stop 73 and an object lens 74, which are loaded onto a carriage 75. An optical disk 76 is arranged above the mobile optical unit 71.
In the optical disk apparatus, a laser beam launched from the stationary optical unit 70 is first irradiated to the rotary mirror 72. The laser beam is reflected by the rotary mirror 72 to cause its optical direction to be changed about 90 degrees. Then, the laser beam passes through the lens iris 73, and is focused by the objective lens 74 to be focused on a recording film of the optical disk 76. The beam reflected by the recording film is changed in its optical axis direction, passes through its original path, and returns to the stationary optical unit 70. The reflected beam is detected by a photo-detector (not shown) in the stationary optical unit 70, thereby causing a signal having been previously recorded in the recording film to be read.
However, in the prior art optical disk apparatus, as shown in FIG. 8, a dislocation occurs between the optical axis of the laser beam launched from the stationary optical unit 70 and the optical center axis of the mobile optical unit 71. That is, a problem exists in that the optical axis L of the laser beam changed in direction by the rotary mirror 72 is dislocated from the optical center axis L' of an optical system consisting of the lens stop 73 and the objective lens 74 of the mobile optical unit 71.
When such dislocation occurs, an intensity distribution 90 of the beam irradiated to the recording film of the optical disk becomes asymmetric as shown in FIG. 9. When the intensity distribution of the beam becomes asymmetric, an offset occurs in tracking error signal and focus error signal during operation. A problem has existed in that, if the asymmetry becomes as extreme as exceeds an allowable range, the control operation of the object lens, that is, the accurate positioning of the object lens cannot be performed, thereby causing signals not be read stably. In the prior art optical disk apparatus, a control to make the dimensional accuracy of each parts higher has been performed to solve such problems, but such problems have not completely solved.